Ultrastructure and phylogeny of Ceratomyxa auratae n. sp. (Myxosporea: Ceratomyxidae), a parasite infecting the gilthead seabream Sparus aurata (Teleostei: Sparidae)

Morphological and Molecular Characterization of Two New Species of Ceratomyxa Thélohan, 1892 (Cnidaria: Myxosporea) from the Marine Ornamental Fish Zanclus cornutus (Linnaeus, 1758) off Lakshadweep Islands, Arabian Sea

PURPOSE

The present study provides the complete morphological and molecular description of two new species of myxosporeans, Ceratomyxa zancli n. sp. and Ceratomyxa cornuti n. sp. infecting the gallbladder of Zanclus cornutus from the Lakshadweep Islands, Arabian Sea.

METHODS

Zanclus cornutus were screened for the presence of myxosporeans, and the recovered myxospores were morphologically characterized using Nomarski Differential Interference Contrast (DIC) optics. The sequences of SSU rDNA were employed for molecular and phylogenetic studies.

RESULTS

Both the parasites exhibited a prevalence of 21% each. C. zancli n. sp. is characterized by broadly cresentic myxospores with convex anterior and slightly concave to straight posterior margins and rounded ends. Spore valves two, unequal, measured 9.6 ± 0.7 μm × 25.2 ± 1.3 μm. Polar capsules two, unequal, spherical, measured 4 ± 0.6 μm × 3.5 ± 0.6 μm. Polar filament exceptionally long and arranged irregularly. Myxospores of C. cornuti n. sp. are elongated with convex anterior and slightly concave to straight posterior margins. Spore valves two, unequal, measured 7.00 ± 0.4 μm × 26.56 ± 1.8 μm. Polar capsules spherical, unequal, measured 3.52 ± 0.2 × 3.36 ± 0.35. Molecular analysis of C. zancli n. sp. (ON818297) and C. cornuti n. sp. (ON818298) resulted in 1469 and 1491 bp long SSU rDNA sequences, respectively. Molecularly C. zancli n. sp. is close to C. diplodae and C. barnesi with 91.39% similarity, while C. cornuti n. sp. appears closer to C. robertsthomsoni with 97.46% similarity. In phylogenetic analyses, C. zancli n. sp. branched separately within the Ceratomyxa clade while C. cornuti n. sp. clustered with C. robertsthomsoni and C. thalassomae.

CONCLUSION

Based on the differences in morphological, morphometric, molecular, and phylogenetic characteristics, as well as differences in the host and geographic location, the above two species of myxosporeans are considered novel. The study forms the first report of a species of Ceratomyxa from Z. cornutus.

Morphological and molecular characterization of Chloromyxum dasyatidis n. sp. (Myxosporea: Chloromyxidae) in the common stingray Dasyatis pastinaca (Linnaeus) from Tunisian waters (Central Mediterranean Sea)

A new species of Chloromyxum Mingazzini, 1890, C. dasyatidis n. sp., is described from the gallbladder of the elasmobranch fish Dasyatis pastinaca (Linnaeus) from the Mediterranean coast off Tunisia. Mature myxospores were subspherical measuring 13.0 ± 0.3 (12.5-13.9) µm in length, 11.3 ± 0.5 (10.2-12.2) µm in width, and 11.8 ± 0.5 (11.4-12.7) µm in thickness. Four pyriform polar capsules 4.4 ± 0.3 (4.0-4.9) µm long and 3.5 ± 0.3 (3.0-3.8) µm wide. Valves were ornamented by 5 to 7 elevated surface ridges and displayed short caudal filaments. Chloromyxum dasyatidis n. sp. had an overall prevalence of infection of 38.5%, with significant seasonal variation, being more prevalent during summer (60.0%) and autumn (70.8%). Phylogenetically, this species grouped within the Chloromyxum sensu stricto lineage, forming a small clade together with the genetically more similar species C. acuminatum and C. myolibati, both from stingray hosts.

Occurrence of two myxosporean parasites in the gall bladder of white seabream Diplodus sargus (L.) (Teleostei, Sparidae), with the morphological and molecular description of Ceratomyxa sargus n. sp

Myxosporeans are widespread cnidarian parasites that usually parasitize fish as part of their complex life cycle, thus constituting a potential threat for the aquaculture industry. White seabream Diplodus sargus (L.) is a commercially valuable sparid fish reared in Southern European aquacultures. Nonetheless, knowledge on myxosporean infections potentially harming the sustainable production of this fish is extremely limited. In this study, a myxosporean survey was conducted on D. sargus specimens reared in two Southern Portuguese fish farms. Two coelozoic myxosporeans were detected infecting the gall bladder, and are herein reported based on microscopic and molecular procedures: Ceratomyxa sargus n. sp. and Zschokkella auratis Rocha et al., 2013, previously described from reared stocks of gilthead seabream Sparus aurata in the same geographic locality. Ceratomyxa sargus n. sp. is the 12^th species of the genus to be reported from Southern European sparids, reinforcing a substantial radiation of Ceratomyxa within this fish family and geographic region. SSU rRNA-based Bayesian inference and maximum likelihood analyses revealed C. sargus n. sp. positioned separately from other sparid-infecting Ceratomyxa spp. reported from Southern European countries, demonstrating that this species does not share a more immediate common ancestor with its closest relatives based on host affinity and geography. The recognition of a novel sparid-infecting lineage within the Ceratomyxa clade strengthens the contention that this genus entered sparid fish multiple times, namely in the Southern European region. The identification of Zschokkella auratis infections in D. sargus demonstrates that host shift has occurred among sparids reared in the Southern Portuguese coast. This agrees with the broad host specificity that is usually attributed to this genus, and that may be suggested to be the outcome of the capacity of the Zschokkella morphotype to undergo host shift/switch based on our findings and the limited molecular data available for this genus. Thus, a better understanding of Zschokkella host-associated diversification and dispersal mechanisms requires the increasing availability of molecular data from infections of the same species occurring in multiple hosts and geographical locations.

Myxidium tunisiensis n. sp. (Myxosporea: Myxidiidae) infecting the rough skate Raja radula Delaroche, 1908 (Rajiformes: Rajidae) from North East Tunisia

A new marine myxosporean, Myxidium tunisiensis n. sp. (Myxosporea: Myxidiidae), is described infecting the gallbladder of the rough skate Raja radula Delaroche, 1908 (Chondrichthyes: Rajidae) harvested from the Bay of Bizerte, Tunisia. Observed stages of the parasite were floating free in the bile. Plasmodia, disporic or polysporic, contain disporic pansporoblasts measuring 23.0-27.2 μm in maximum diameter and 21.0-25.5 μm in minimum diameter. Mature myxospores, which are elongated, typically fusiform measured 18.6 ± 1.7 (17.2-22.0) μm in length, 8.6 ± 1.2 (7.2-11.2) μm in width and 8.2 ± 0.9 (6.4-10.1) in thickness. Myxospore valves are symmetrical with 9-10 longitudinal striations. Two polar capsules, pyriform, were equal in size, measuring 5.8 ± 0.4 (5.2-6.7) μm in length and 3.1 ± 0.2 (3.0-3.2) μm in width, with 5-6 polar filament turns. The infection was prevalent throughout the year with the highest prevalence in autumn (81.8%) and the lowest in winter (32.3%). The seasonal prevalence of M. tunisiensis n. sp. in the Bay of Bizerte appeared to fluctuate according to seawater temperature. The morphological and morphometrical differences with all Myxidium spp. described so far, complemented by molecular data, prove clearly that the present species is a new member of the genus Myxidium. The SSU rDNA phylogenetic analyses revealed that Myxidium tunisiensis n. sp. clustered within the oligochaete-gallbladder clade in a basal position to the marine subclade of Myxidium baueri and Myxidium coryphaenoideum. While the new species branching pattern is stable in the ML and the BI analyses, it changed in the MP analysis. This is the first molecular study of a Myxidium species infecting an elasmobranch host inhabiting the Mediterranean Sea.

Molecular and morphological description of Ceratomyxa scophthalmi sp. nov. (Myxozoa) infecting Scophthalmus maeoticus and first report of Myxidium finnmarchicum in the Black Sea

In the present study, 2 species of myxozoan parasites, the novel Ceratomyxa scophthalmi sp. nov. and Myxidium finnmarchicum, were documented from the gallbladder of Scophthalmus maeoticus inhabiting the Turkish Black Sea coast at Sinop. C. scophthalmi sp. nov. had mostly spherical, clavate, and fine-grained polymorphic plasmodia that ranged in diameter from 16.0 to 29.0 µm. Spores were arcuate with a convex anterior margin and concave posterior. Valves of spores were highly elongated and unequal in thickness with one valve 1.1-1.3 times thicker than the other. Valves narrowed gradually toward slightly truncated ends. The mean (range) dimensions of spores were 9.4 (8.5-10.0) µm in length and 49.6 (44.5-55.0) µm in thickness, with polar capsules that were 3.1 (2.7-3.5) µm in length and 3.2 (2.7-3.5) µm in width. Polar filaments were coiled with 4-5 turns. Large numbers of immature forms of C. scophthalmi sp. nov., which were often 'crumpled', and mature forms were found together in the gallbladder bile. Along with morphological differences, phylogenetic analysis based on 18S rDNA, including pairwise nucleotide similarities with other related Ceratomyxa species, suggests C. scophthalmi as a novel species. Moreover, this report provides the first morphological and molecular descriptions of M. finnmarchicum outside of its original geographical location and type host species.

Morphological and molecular characterization of Ceratomyxa binhthuanensis n. sp. (Myxosporea: Ceratomyxidae) from the gall bladder of blacktip grouper Epinephelus fasciatus (Perciformes: Serranidae) in the East Sea of Vietnam

A new myxozoan species, Ceratomyxa binhthuanensis n. sp. (Myxosporea: Ceratomyxidae), was found in the gall bladder of blacktip grouper Epinephelus fasciatus (Perciformes: Serranidae) in the East Sea of Vietnam. Myxospores were observed floating free in the gall bladder of 3 out of 20 fish examined (15%). Mature myxospores were elongate and slightly crescent-shaped and measured 12.2 ± 1.3 (10.8-16.0) μm in thickness and 5.8 ± 0.6 (4.8-6.9) μm in length, with two smooth equal shell valves. The two polar capsules were spherical and equal in size, measuring 2.6 ± 0.3 (2.3-2.9) μm in diameter. The posterior angle was slightly concave, 153.7° ± 5.6° (148.9°-166.0°). Molecular analysis of SSU rDNA sequence showed that Ceratomyxa binhthuanensis n. sp. differs from other Ceratomyxa spp. available in GenBank. Phylogenetic analysis indicated that C. binhthuanensis n. sp. was closely related to three species, Ceratomyxa nolani, Ceratomyxa yokoyamai, and Ceratomyxa cutmorei, which also infect fish hosts of the genus Epinephelus.

Two novel myxosporean parasite species of Ceratomyxa Thélohan, 1892 from the banded cusk-eel Raneya brasiliensis (Kaup) (Ophidiiformes: Ophidiidae) off Patagonia, Argentina

We described two novel myxozoan parasite species Ceratomyxa argentina n. sp. and Ceratomyxa raneyae n. sp. from the gall bladder of Raneya brasiliensis (Kaup) from the Patagonian coast of Argentina. Both species can be distinguished from other ceratomyxids by myxospore and polar capsule (nematocyst) morphology and morphometry, fish host and geographic locality. Phylogenetic reconstruction using ssrDNA gene sequences showed that the two new species are placed in a long-branching ceratomyxid clade which also include Ceratomyxa appendiculata Thélohan, 1892, Ceratomyxa anko Freeman, Yokoyama and Ogawa, 2008, Ceratomyxa pantherini Gunter, Burger and Adlard, 2010 and Pseudoalataspora kovalevae Kalavati, MacKenzie, Collins, Hemmingsen and Brickle, 2013. This study documents additional biodiversity of marine myxozoans in the South Atlantic, a region still largely unexplored for this group of parasitic cnidarians.

Morphological and molecular analysis of Henneguya lagunensis n. sp. (Cnidaria, Myxosporea) parasitizing the gills of Eugerres brasilianus from Brazil

Plasmodia containing myxospores belonging to the genus Henneguya Thélohan, 1892 were found in the gills of Eugerres brasilianus (Cuvier, 1830). Despite the economic importance, few parasitological studies have been done with this species. We describe Henneguya lagunensis n. sp. using morphological and molecular data. The mature myxospores were rounded, measuring 29.1 ± 2.2 μm in total length, 8.2 ± 1.0 μm in body length, 7.9 ± 0.2 μm in body width, 20.7 ± 2.4 μm in tail length and 4.8 ± 1.0 μm in thickness. The polar capsules measured 3.3 ± 0.4 in length and 1.7 ± 0.3 μm in width. Polar filaments had 4-5 turns, helical. Phylogenetic analysis showed Henneguya lagunensis n. sp. as a sister species of Henneguya cynoscioni Dyková, Buron, Roumillat and Fiala, 2011, within a clade that contained mostly Henneguya species that parasitize marine fish of the order Perciformes. This is the first report of a species of Henneguya parasitizing Eugerres brasilianus.

Involvement of sphaeractinomyxon in the life cycle of mugiliform-infecting Myxobolus (Cnidaria, Myxosporea) reveals high functionality of actinospore morphotype in promoting transmission

Four new actinospore types belonging to the sphaeractinomyxon collective group (Cnidaria, Myxosporea) are described from the coelomic cavity of a marine Baltidrilus sp. (Oligochaeta, Naididae) inhabiting a northern Portuguese estuary. Host identification supports the usage of marine oligochaetes, namely of the family Naididae Ehrenberg, 1828, as definitive hosts for myxosporeans inhabiting estuarine/marine environments. The absence of mixed infections in the host specimens analysed is suggested to reflect the influence of host-, parasite- and environmental-related factors regulating myxosporean-annelid interactions. Molecular analyses matched the SSU rDNA sequences of three of the four new types with those of mugiliform-infecting Myxobolus spp., namely Myxobolus mugiliensis and a Myxobolus sp. from flathead grey mullet Mugil cephalus, and Myxobolus labrosus from thicklip grey mullet Chelon labrosus. These results directly link, for the first time, the sphaeractinomyxon collective group to a myxospore counterpart, further confirming their previously hypothesized specific involvement in the life cycle of myxobolids that infect mullets. Acknowledging this life cycle relationship, the functionality of the sphaeractinomyxon morphotype is suggested to have been decisive for the evolutionary hyperdiversification of the genus Myxobolus in mullets. Unlike other actinospore morphotypes, sphaeractinomyxon lack valvular processes, which implies a limited capability for buoyancy. Considering the benthic-feeding nature of mullets, this feature is most likely crucial in promoting successful transmission to the vertebrate host.

Morphology, seasonality and molecular characterization of Ceratomyxa draconis n. sp. parasite of Trachinus draco (L.) from the Bay of Bizerte, Tunisia

The specimens of Trachinus draco collected from the Bay of Bizerte were found to be infected with a new Ceratomyxa species described as Ceratomyxa draconis n. sp. The sequence of small subunit ribosomal RNA gene obtained in this study differs from other Ceratomyxa sequences available in GenBank. Mature spores of this species were elongated and crescent-shaped in sutural view, measuring 7.4 ± 0.77 (6.4-8.0) μm in thickness and 30.8 ± 1.65 (28.8-32.8) μm in width. The polar capsules were spherical, equal in size, and measuring 3.3 ± 0.2 (3.6-4.0) μm in diameter. The Ceratomyxa draconis n. sp. showed a clearly seasonal variation of prevalence with highest prevalence noted during summer months.

Ceratomyxa mennani n. sp. (Myxosporea: Bivalvulida) parasitizing the gallbladder of the dusky grouper Epinephelus marginatus (Serranidae) from Tunisian waters

Ceratomyxa mennani n. sp. is a new coelozoic Ceratomyxa species found in the gallbladder of Epinephelus marginatus from the Gulf of Tunis, Tunisia. Mature plasmodia were disporic, ovoid in shape measuring 9-12 μm in width and 11-14 μm in length. Mature myxospores were slightly crescent-shaped with almost straight posterior margin, measuring 5.8 ± 0.2 (5.4-6.1) μm in length and 12.7 ± 0.3 (11.9-13.0) μm in thickness. The two valves were unequal with rounded ends. Polar capsules were spherical, equal in size with 2.1 ± 0.2 (1.9-2.6) μm in diameter. The binucleated sporoplasm filled the entire cavity of the myxospore. Molecular analysis of SSU rDNA sequences indicated that C. mennani n. sp. was distinct from all other Ceratomyxa sequences in GenBank. Phylogenetic analysis revealed that C. mennani n. sp. clustered with Ceratomyxa species infecting Epinephelinae fishes. Seasonal prevalence of infection over one year was significantly higher in winter and the lowest in autumn. This is the third report of Ceratomyxa species infecting the gallbladder of Epinephelus marginatus from Tunisia and the first study to include molecular data.

Characterisation of sphaeractinomyxon types (Cnidaria: Myxozoa) from marine and freshwater oligochaetes in a Portuguese estuary, with the demise of the endocapsa collective group

Six types of sphaeractinomyxon are reported from the coelomic cavity of oligochaetes collected from the Minho River estuary in northern Portugal. Four new types are morphologically and molecularly described from freshwater species belonging to the genera Psammoryctides Hrabě and Potamothrix Vejdovský et Mrázek in the upper estuary, thus significantly increasing the number of known freshwater sphaeractinomyxon. In the lower estuary, sphaeractinomyxon types 8 and 10 of Rangel et al. (2016) are recorded infecting the marine oligochaete Tubificoides pseudogaster (Dahl). A single specimen of T. pseudogaster further displayed infection by one of the four new types found in the upper estuary, suggesting the involvement of sphaeractinomyxon in the life cycles of myxosporean species that infect migratory fish hosts. The acquisition of these second hosts is proposed to have allowed the myxosporean counterparts of sphaeractinomyxon to cross environmental barriers and conquer new habitats. Phylogenetic analyses of the SSU rRNA gene reveal the four new types clustering within the monophyletic clade of mugiliform-infecting myxobolids, strengthening the previously proposed involvement of the sphaeractinomyxon collective group in the life cycles of this specific group of myxosporeans. Endocapsa types also cluster within the latter clade, having actinospores that differ from those of sphaeractinomyxon only in the presence of valvular swellings that do not change when in contact with water. In this study, however, one type was found displaying actinospores with and without valvular swellings in the same oligochaete specimen. This overlap in actinospore morphology is given as grounds for the demise of the endocapsa collective group.

Myxozoan biodiversity in mullets (Teleostei, Mugilidae) unravels hyperdiversification of Myxobolus (Cnidaria, Myxosporea)

Mullets are ecologic and commercially important fish species. Their ubiquitous nature allows them to play critical roles in freshwater and marine ecosystems but makes them more vulnerable to diseases and parasitic infection. In this study, a myxozoan survey was performed on three species of mullet captured from a northern Portuguese river. The results disclose a high biodiversity, specifically due to the hyperdiversification of Myxobolus. Thirteen new species of this genus are described based on microscopic and molecular procedures: 7 from the thinlip grey mullet Chelon ramada, 2 from the thicklip grey mullet Chelon labrosus, and 4 from the flathead grey mullet Mugil cephalus. Myxobolus exiguus and Ellipsomyxa mugilis are further registered from their type host C. ramada, as well as six more myxospore morphotypes that possibly represent distinct Myxobolus species. Overall, the results obtained clearly show that the number of host-, site- and tissue-specific Myxobolus spp. is much higher than what would be expected in accordance to available literature. This higher biodiversity is therefore discussed as either being the result of the usage of poor discriminative criteria in previous studies, or as being a direct consequence of the biological and ecological traits of the parasite and of its vertebrate and invertebrate host communities. Bayesian inference, maximum likelihood and maximum parsimony analyses position the new species within a clade comprising all other Myxobolus spp. that infect mugiliform hosts, thus suggesting that this parasitic group has a monophyletic origin. Clustering of species in relation to the host genus is also revealed and strengthens the contention that the evolutionary history of mugiliform-infecting Myxobolus reflects that of its vertebrate hosts. In this view, the hyperdiversification of Myxobolus in mullet hosts is hypothesized to correlate with the processes of speciation that led to the ecological plasticity of mullets.

New actinosporean description prompts union of the raabeia and echinactinomyxon collective groups (Cnidaria, Myxozoa)

We describe, morphologically and molecularly, a new actinosporean from the intestinal epithelium of the freshwater oligochaete Ilyodrilus templetoni in the upper estuary of the River Minho, Northern Portugal. Mature actinospores resembled both echinactinomyxon and raabeia types, emphasizing the previously known lack of a clear boundary between these 2 collective groups. Historically, raabeia and echinactinomyxon types have been differentiated solely based on the shape of the valvular processes being curved or straight, respectively. Our observations, however, show that this morphological character is too variable for distinguishing between these 2 collective groups, since the actinospores of the raabeia described here displayed valvular processes that could either be straight, downward or upward curved. Several similar cases can be found in the available literature. Considering this overlap in actinospore morphology, we propose that echinactinomyxon be deemed invalid and its types be included in raabeia, as the latter constitutes the older of the 2 groups. Known echinactinomyxon types, however, should not be renamed as raabeia, as this would create unnecessary confusion. Accordingly, a more comprehensive definition of the raabeia collective group is provided. Phylogenetic analyses revealed polyphyletic clustering of raabeia/echinactinomyxon types among members of the myxosporean suborders Variisporina and Platysporina, reiterating the lack of agreement between actinosporean morphotypes and myxosporean genera. The new type described here specifically clusters within the Paramyxidium clade, alongside other SSU rDNA sequences of raabeia, echinactinomyxon, aurantiactinomyxon and synactinomyxon. Considering that most Paramyxidium spp. parasitize Anguilla anguilla (Linnaeus, 1758), future myxozoan surveys in the River Minho should include this species.

Morphological and molecular characterization of myxobolids (Cnidaria, Myxozoa) infecting cypriniforms (Actinopterygii, Teleostei) endemic to the Iberian Peninsula

The Iberian Peninsula provides a unique freshwater ecosystem for native and endemic cypriniforms to thrive. Despite cypriniforms being hosts to multiple myxobolids worldwide, little research has been performed in this geographic location. In this study, the examination of three Iberian endemic cypriniforms showed that myxosporean richness in the Iberian Peninsula is underestimated, with three new and one known myxobolid species being reported based on morphological and molecular data (SSU). Myxobolus arcasii n. sp. is described from the kidney and gonads of the "bermejuela" Achondrostoma arcasii, M. duriensis n. sp. from the gills of the Northern straight-mouth nase Pseudochondrostoma duriense, and Thelohanellus paludicus n. sp. from the intestine of the Southern Iberian spined-loach Cobitis paludica. Myxobolus pseudodispar Gorbunova, 1936 is further reported from several organs of P. duriense, and from the spleen of A. arcasii. The occurrence of M. pseudodispar in endemic Iberian species reveals that host-shift followed its co-introduction with central European leuciscids into this geographic location. Several other myxobolids originally described from barbels in central Europe have also been reported from the Iberian endemic cypriniform Luciobarbus bocagei. Nonetheless, except for M. musculi, the identification of these myxobolids in L. bocagei is here shown to be dubious and require molecular confirmation. Phylogenetic analyses reveal M. arcasii n. sp. and M. duriensis n. sp. clustering within different lineages of leuciscid-infecting species, showing that myxobolids entered Leuciscidae as hosts multiple times during their evolution. Constituting the first myxobolid reported from the subfamily Cobitinae, Thelohanellus paludicus n. sp. stands alone in the tree topology.

Molecular data infers the involvement of a marine aurantiactinomyxon in the life cycle of the myxosporean parasite Paramyxidium giardi (Cnidaria, Myxozoa)

An aurantiactinomyxon type is described from the marine naidid Tubificoides pseudogaster (Dahl, 1960), collected from the lower estuary of a Northern Portuguese River. This type constitutes the first of its collective group to be reported from Portugal, and only the fourth described from a marine oligochaete worldwide. Extensive morphological comparisons of new aurantiactinomyxon isolates to all known types without available molecular data are proposed to be unnecessary, given the artificiality of the usage of morphological criteria for actinosporean differentiation and the apparent strict host specificity of the group. Recognition of naidid oligochaetes as the hosts of choice for marine types of aurantiactinomyxon and other collective groups, suggests that the family Naididae played a preponderant role in the myxosporean colonization of estuarine communities. Molecular analyses of the type in study further infer its involvement in the life cycle of Paramyxidium giardi (Cépède, 1906) Freeman and Kristmundsson, 2018, a species that infects the kidney of European eel Anguilla anguilla (Linnaeus, 1758) and that has been reported globally, including from Portuguese waters. The low intraspecific difference registered in relation to Icelandic isolates of P. giardi (0.6%) is hypothesized to result from the emergence of genotypically different subspecies due to geographic isolation.

Phylogeny and comprehensive revision of mugiliform-infecting myxobolids (Myxozoa, Myxobolidae), with the morphological and molecular redescription of the cryptic speciesMyxobolus exiguus

Mullets inhabit a wide range of habitats from tropical to temperate regions and play a critical role in their ecosystems. This commercially important fish group constitutes a significant source of food in several geographic regions, and the production of some species for consumption is an increasing trend. About 64 myxosporean species have been reported in mullets, some of which are cryptic, as is the case ofMyxobolus exiguus, andM. muelleri. This paper provides, for the first time, a detailed and critical revision of the data available for myxobolids reported in mullets, determining the species that havebona fidemugiliform fish hosts, in accordance with the original species descriptions, the available molecular data and the currently accepted taxonomic and phylogenetic criteria. Phylogenetic analyses using Bayesian inference and maximum-likelihood methodologies suggest that the evolutionary history of myxobolids withbona fidemugiliform fish hosts reflects that of its vertebrate hosts, while reinforcing known evolutionary factors and old systematic issues of the clade of myxobolids. A comprehensive morphological, ultrastructural and molecular redescription is also provided for the cryptic speciesM. exiguus, from infections in the visceral peritoneum of the thinlip-grey mulletChelon ramadain the River Minho, Portugal.

Ceratomyxa gouletti n. sp. (Myxosporea: Ceratomyxidae), a parasite of the red scorpionfish Scorpaena scrofa (L.) from Tunisian waters

Ceratomyxa gouletti n. sp. is a new parasite described from the gallbladder of the red scorpionfish Scorpaena scrofa (Scorpaeniformes: Scorpaenidae) collected from La Goulette in the Northeast of Tunisia. The parasite develops disporic plasmodia, elliptical to ovoid in shape, measuring up to 33.1 ± 3.6 (28.0-38.2) μm in length and 12.5 ± 2.1 (11.3-14.0) μm in width. Mature spores are elongated transversely and crescent-shaped with rounded ends and unequal shell valves, measuring 8.1 ± 1.27 (7.2-9.0) μm in length and 32.0 ± 2.5 (27.0-38.2) μm in thickness. Sutural line is straight and visible between valves. Polar capsules are subspherical with 3.15 ± 0.63 (2.7-3.6) μm long and 1.9 ± 0.14 (1.8-2.0) μm wide. Posterior spore angle is slightly concave 160°-175°. Molecular analysis based on the small subunit 18S rDNA sequence shows that C. gouletti n. sp. is different from all other ceratomyxid species DNA sequences in GenBank. Phylogenetic trees clustered the new species with long-branching Ceratomyxa species, and it was closely related to the species Ceratomyxa longipes from two gadid fish hosts with 89% bootstrap support.

Synopsis of the species of Ceratomyxa Thélohan, 1892 (Cnidaria, Myxosporea, Ceratomyxidae) described between 2007 and 2017

A synopsis of the species of Ceratomyxa Thélohan, 1892 (Cnidaria, Myxosporea, Ceratomyxidae) described between 2007 and 2017 is presented, including 83 nominal species. For each species, the most important morphological and morphometric features are indicated in tabulated format. Included are also the site of infection within the host, and geographical location, plus a full bibliography of the original records of species. Molecular data (GenBank accession numbers) are also provided whenever possible.

Ceratomyxa azevedoi n. sp. (Myxozoa: Myxosporea) parasitizing the gallbladder of Lutjanus ehrenbergii in the Arabian Gulf

A novel myxosporean species, Ceratomyxa azevedoi sp. n. is described from the gallbladder of the blackspot snapper, Lutjanus ehrenbergii (Peters), captured from the Arabian Gulf off Saudi Arabia. A total of 45 (26.8%) out of 168 fish specimens were found to be infected with Ceratomyxa azevedoi sp. n., the highest prevalence being observed in winter (42.9%, 18/42) and the lowest in autumn (11.9%, 5/42). Mature spores appeared as crescent to slightly elliptical-shaped, measuring 5-7 (6) μm in length and 12 (10-14) μm in thickness, with spherical polar capsules containing three polar filament coils. The morphometric and morphological comparison with similar species revealed the taxonomic novelty of this form, suggesting that it should be considered as new species. The phylogenetic analysis of C. azevedoi sp. n., based on partial SSU rDNA sequences, revealed close genetic relatedness to C. buri with 91.3% homogeneity and to C. hamour, with 90.1% homogeneity.

Ultrastructure and phylogeny of Ceratomyxa diplodae (Myxosporea: Ceratomyxidae), from gall bladder of European seabass Dicentrarchus labrax

The myxosporean parasite Ceratomyxa diplodae Lubat et al. 1989 sensu Sitjà-Bobadilla & Álvarez-Pellitero, 1993, originally described from the annular seabream Diplodus annularis in the Adriatic Sea, has subsequently been reported from several other sparid hosts, and also a moronid fish, the European seabass Dicentrarchus labrax from the Mediterranean Sea. Here, molecular identity and additional morphological data are given for this parasite infecting the gall bladder of D. labrax in a southern Portuguese fish farm. In the bile, disporic plasmodia were spherical to subspherical with a smooth surface membrane. Most myxospores were crescent-shaped, 5.1 ± 0.5 (4.8-6.7) µm long (mean ± SD) and 21.9 ± 1.0 (20.4-23.9) µm thick; a few were more arcuate, 5.7 ± 0.4 (5.3-6.3) µm long and 17.3 ± 1.0 (16.3-19.1) µm thick. The wall consisted of 2 symmetrical valves united along a slightly curved suture line, with moderately tapering to rounded ends. Two spherical polar capsules, measuring 2.9 ± 0.3 (2.5-3.4) µm in diameter, contained a polar filament forming 8 to 9 coils organized in 2 rows. Host species, tissue tropism, and myxospore morphology supported species identification. Phylogenetic analyses of the small subunit ribosomal RNA sequence positioned the parasite among most sparid-infecting Ceratomyxa spp., suggesting the existence of a common ancestor for these species. The acquisition of molecular data from infections of C. diplodae in its original host and in other sparids is essential in order to ascertain if the morphological and biological variations found among reports of this parasite are intra- or inter-specific.

Morphological description and phylogeny of Ceratomyxa scorpaeni n. sp. (Myxosporea: Ceratomyxidae) infecting the gallbladder of Scorpaena porcus (L.) (Scorpaeniformes: Scorpaenidae) from the bay of Bizerte in Tunisia

A new marine myxosporean species Ceratomyxa scorpaeni n. sp. is described using morphological characteristics and small subunit ribosomal DNA (rDNA) sequence data. The parasite was found infecting the gallbladder of Scorpaena porcus Linnaeus, 1758 collected from the Bay of Bizerte. Mature plasmodia were disporous free floating in the bile. Spores were transversely elongated and crescent-shaped with unequal shell valves and measured 7.6 ± 0.2 (7.2-8.0) μm in length and 32.8 ± 0.3 (21.6-44.0) μm in thickness. Two sub-spherical polar capsules equal in size, situated at the same level and measured 3.0 ± 0.2 (3.0-3.2) μm in length and 2.4 ± 0.3 (2.3-3.3) μm in width. The infection with C. scorpaeni n. sp. was prevalent throughout the year with a maximum prevalence of infection during spring and summer. Molecular analysis of the SSU rRNA gene confirmed the parasite as a new member of the genus Ceratomyxa and showed close relationship with the species of Ceratomyxa infecting the gallbladders of Sparidae from the Mediterranean Sea. This is the first report of Ceratomyxa species from the gallbladder of S. porcus in Tunisian coastal waters.

Parasites of marine, freshwater and farmed fishes of Portugal: a review

Abstract An extensive literature review is made of the parasites in marine and freshwater fish in mainland Portugal, the Portuguese archipelagos of the Azores and Madeira, as well as in farmed fish. The host(s) of each parasite species, its location in the host, site of capture of the host, whenever possible, and all the available bibliographic references are described. The economic importance of some parasites and the zoonotic relevance of some parasitic forms are discussed. A general overview of the data is provided, and some research lines are suggested in order to increase and complement the current body of knowledge about the parasites of fish from Portugal.

Ceratomyxa tunisiensis n. sp. (Myxosporea: Bivalvulida) from the Gallbladders of Two Carangid Fish Caught Off the Coast of Tunisia

A new coelozoic Myxozoan species, Ceratomyxa tunisiensis n. sp., was found infecting the gallbladders of two carangid fish, Caranx rhonchus and Trachurus trachurus (Perciforme, Carangidae), from the Gulf of Gabès, on the southern coast of Tunisia. The parasite develops in spherical mono-, diplo-, or polysporic tropozoites in the gallbladder of the hosts. Mature spores are typical of the genus Ceratomyxa. They are transversely elongated and narrowly crescent-shaped with a slightly convex anterior and concave posterior, and measure 23 ± 0. 27 (20-25) μm width × 6 ± 0.26 (5-8) μm in length. Spore shell valves are symmetrical with rounded ends. Two spherical polar capsules situated on either side of the sutural line measure 2.2 μm (2.0-3.0) in diam. Periodical sampling of C. rhonchus and T. trachurus from Marsh 2012 to February 2013 showed that infection due to C. tunisiensis occurs in 59% and 69% of the examined fish, respectively. Molecular analysis based on the small subunit (SSU) rRNA sequence shows high genetic divergence with all other ceratomyxid species. A Maximum Likelihood phylogenetic tree shows association with the species C. leatharjecketi Fiala, kova, Kodadkova, Freeman, Bartošova-Sojkova, and Atkinson, 2015 reported from the gallbladder of Aluterusmonoceros (L.) caught in the Andaman Sea, off Malaysia. Nonetheless, the SSU rRNA sequences of C. tunisiensis and C. leatharjecketi have only a 90% similarity.

Testicular myxosporidiasis and ultrastructural characteristics of Myxobolus bufonis (Myxobolidae) infecting the Egyptian toad Bufo regularis (Bufonidae). A light and electron microscopic study

The phylum Myxozoa comprises more than 2180 species, almost all of which are considered to be obligate parasites of aquatic fishes and amphibians. They are dangerous pathogens responsible for severe economic losses. From March to September 2014, 40 adult male Bufo regularis (Bufonidae) captured from different areas at Giza province, Egypt, were surveyed for myxosporean parasitic infection. Of these, 22 (55%) were infected by histozoic plasmodia, which produced spores after rupture belonging to Myxosporidia. The present investigation introduced a new data for the recorded parasite observed by light and transmission electron microscopy. The infection was diagnosed as large clusters of macroscopic plasmodia embedded in the testicular tissue causing distortion at the site of infection. The host reaction was manifested by the encapsulation of the plasmodia with a thick layer of connective tissue. Plasmodia were whitish in color, elliptical to ovoid in shape measuring 0.54 ± 0.2 (0.34-0.63) mm in diameter. The spores were subspherical, reaching 7.1 ± 0.2 (6.2-8.4) μm in length and 6.3 ± 0.2 (5.8-7.0) μm in width with two equal-sized polar capsules regularly arranged at the anterior pole of each spore. They were 3.4 ± 0.2 (3.0-4.2) μm in length and 1.9 ± 0.2 (1.6-2.4) in width with 6-8 turns of polar filaments. Ultrastructural analysis showed that the plasmodia were surrounded by a plasma membrane with numerous projections and pinocytotic channels extended toward the host cell. The generative cells and the different developmental stages were arranged at the periphery of the plasmodia while immature and mature spores were centrally arranged. Sporogenesis, capsulogenesis, valvogenesis, and spore maturation of the present parasite were also described.